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Lecture 5 Plutonic Structures and Field Relationships

Friday, February 4th, 2005

Figure 4-20. Schematic block diagram of some intrusive bodies.

Plutonic Structures and Field Relationships

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Figure 4-21. Kangâmiut dike swarm in the SøndreStrømfjord region of SE Greenland. From Escher et al. (1976), Geology of Greenland, © The Geological Survey of Denmark and Greenland. 77-95.

Figure 4-22. a. Radial dike swarm around Spanish Peaks, Colorado. After Knopf (1936), Geol. Soc. Amer. Bull., 47, 1727-1784. b. Eroded remnant of a volcanic neck with radial dikes. Ship Rock, New Mexico. From John Shelton © (1966) Geology Illustrated. W. H. Freeman. San Francisco.

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Figure 4-23. The formation of ring dikes and cone sheets. a.Cross section of a rising pluton causing fracture and stoping of roof blocks. b. Cylindrical blocks drop into less dense magma below, resulting in ring dikes. c. Hypothetical map view of a ring dike with N-S striking country rock strata as might result from erosion to a level approximating X-Y in (b). d. Upward pressure of a pluton lifts the roof as conical blocks in this cross section. Magma follows the fractures, producing cone sheets. Original horizontal bedding plane shows offsets in the conical blocks. (a), (b), and (d) after Billings (1972), Structural Geology. Prentice-Hall, Inc. (c) after Compton (1985), Geology in the Field. ©Wiley. New York.

Figure 4-24. a. Map of ring dikes, Island of Mull, Scotland. After Bailey et al. (1924), Tertiary and post-tertiary geology of Mull, Loch Alineand Oban. Geol. Surv. Scot. Mull Memoir. Copyright British Geological Survey.

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Figure 4-24. b. Cone sheets in the same area of Mull, after Ritchey (1961), British Regional Geology. Scotland, the Tertiary Volcanic Districts. Note that the yellow felsite ring dike in part (a) is shown as the red ring in the NW of part (b). British Geological Survey.

Figure 4-25. Types of tabular igneous bodies in bedded strata based on method of emplacement. a. Simple dilation (arrows) associated with injection. b. No dilation associated with replacement or stoping. © John Winter and Prentice Hall.

Structures and Field Relationships

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Figure 4-26. Shapes of two concordant plutons. a. Laccolith with flat floor and arched roof. b. Lopolith intruded into a structural basin. The scale is not the same for these two plutons, a lopolith is generally much larger. © John Winter and Prentice Hall.

Structures and Field Relationships

Figure 4-27. Gradational border zones between homogeneous igneous rock (light) and country rock (dark). After Compton (1962), Manual of Field Geology. © R. Compton.

Structures and Field Relationships

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Figure 4-28. Marginal foliations developed within a pluton as a result of differential motion across the contact. From Lahee (1961), Field Geology. © McGraw Hill. New York.

Structures and Field Relationships

Figure 4-29. Continuity of foliation across an igneous contact for a pre- or syn-tectonic pluton. From Compton (1962), Manual of Field Geology. © R. Compton.

Structures and Field Relationships

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Figure 4-30. Block diagram several kilometers across, illustrating some relationships with the country rock near the top of a barely exposed pluton in the epizone. The original upper contact above the surface is approximated by the dashed line on the front plane. From Lahee (1961), Field Geology. © McGraw Hill. New York.

Structures and Field Relationships

Figure 4-31. a. General characteristics of plutons in the epizone, mesozone, and catazone. From Buddington (1959), Geol. Soc. Amer. Bull., 70, 671-747.

Structures and Field Relationships

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Figure 4-32. Developmental sequence of intrusions composing the Tuolumne Intrusive Series (after Bateman and Chappell, 1979), Geol. Soc. Amer. Bull., 90, 465-482. a. Original intrusion and solidification of marginal quartz diorite. b. Surge of magma followed by solidification of Half Dome Granodiorite. c. Second surge of magma followed by solidification of porphyritic facies of Half Dome Granodiorite. d. Third surge of magma followed by solidification of Cathedral Peak Granodiorite and final emplacement of Johnson Granite Porphry.

Structures and Field

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Figure 4-33. Block diagram of subsurface salt diapirs in Northern Germany. After Trusheim (1960), Bull. Amer. Assoc. Petrol. Geol., 44, 1519-1540 © AAPG.

Structures and Field Relationships

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Figure 4-34. Diagrammatic illustration of proposed pluton emplacement mechanisms. 1- doming of roof; 2- wall rock assimilation, partial melting, zone melting; 3- stoping; 4- ductile wall rock deformation and wall rock return flow; 5- lateral wall rock displacement by faulting or folding; 6- (and 1)- emplacement into extensional environment. After Paterson et al. (1991), Contact Metamorphism. Rev. in Mineralogy, 26, pp. 105-206. © Min. Soc. Amer.

Structures and Field Relationships

Figure 4-35. Sketches of diapirs in soft putty models created in a centrifuge by Ramberg (1970), In Newell, G., and N. Rast, (1970) (eds.), Mechanism of Igneous Intrusion. Liverpool Geol. Soc., Geol. J. Spec. Issue no. 2.

Structures and Field Relationships

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Figure 4-36. Diagrammatic cross section of the Boulder Batholith, Montana, prior to exposure. After Hamilton and Myers (1967), The nature of batholiths. USGS Prof. Paper, 554-C, c1-c30.

Structures and Field Relationships

Figure 4-37. Schematic section through a hydrothermal system developed above a magma chamber in a silicic volcanic terrane. After Henley and Ellis (1983), Earth Sci. Rev., 19, 1-50. Oxygen isotopic studies have shown that most of the water flow (dark arrows) is recirculated meteoric water. Juvenile magmatic water is typically of minor importance. Elsevier Science.